The mach system is different than most car stereo systems. To keep your speakers, you will need a device to match impedance between the existing stuff and your new stuff. You should be able to use your existing wires with available adapters, or if you are not planning on returning it to stock, just cut off the current connecters.
04 Mustang GT vert basically stock
88 Dodge Ramcharger 4X4 for those things a Mustang just can't (or shouldn't?) do.
98 Ford Taurus SE Comfort --- wify's ride.